Mg—Li based alloy has low density (1300˜1600 kg/m3), high specific strength and stiffness, good damping capacity and excellent electromagnetic shielding properties, as one of the lightest non-toxic metallic materials they are widely used in aerospace, transportation applications. In the binary Mg—Li alloy system, by increase of Li to certain amount, a series of phase transformation will take place as: α(hcp)→α+β→β(bcc), see FIG. 1. These phase transformation can improve alloy ductility as the alloy elongation will increase about 40%. However, Mg—Li alloy has low strength and creep resistance, which limits the application of Mg—Li alloys.
The composite strengthening approach is probably the feasible way to increase strength and to prevent mechanical properties degradation of Mg—Li alloys. Compared with Mg—Li-based alloys, composites can maintain alloy's own properties such as good electrical conductivity, thermal conductivity, excellent cold and hot processing performance, low density, high specific stiffness, high specific strength, good wear, high temperature resistance, excellent damping properties and electromagnetic shielding performance, the alloy strength and creep resistance has largely improved. Hence, Mg—Li composites have became one of the most popular materials used in many applications. Like other composites, three main strengthening methods used in Mg—Li alloy are: fibers, whiskers, and particles strengthening, and the strengthening materials are SiC, B4C, Al2O3, TiC and B. These strengthening materials can be used in Mg—Li alloy singly or coupled together, e.g SiC particles/Al2O3 whiskers mixed, to improve Mg—Li alloy mechanical properties. Although the Mg—Li alloy composites have excellent mechanical properties, some material ductility and elongation were sacrificed. Research results show that, the wetting properties and chemical compatibility between Mg—Li alloy and ceramics are very good to form an ideally alloy/ceramic interface, and the ductility of the ceramics has large impact on composites ductility and plasticity. Hence, to choose a ceramic with certain stain change capability in Mg—Li composites has large influence on material properties.
Intermetallics materials have some metallic material properties such as the metallic colour, electrical conductivity and thermal conductivity, hence they are be choose as the strengthening materials used in Mg—Li composites to form a good wetted and high chemical compatibility interface. In additions, intermetallic material has excellent specific strength and toughness, they can be used in high temperatures. Compared to ceramic reinforced composites material, using intermetallics as the strengthener can also improve composites plasticity and ductility, it can be a very good strengthener materials used in Mg—Li composites applications.
Patent No. 200910082581.7 mentions an ultrafine rare earth intermetallic compounds reinforced metal matrix composites. This composite using the reinforced intermetallic particles with particle size around 0.1˜3 μm, the materials has excellent plasticity and the tensile strength was increased by 20%˜40%. Although the composites has good properties, but the small intermetallic particles in composites are easily clusters and agglomerations with poor metal/intermetallic interface interfacial bonding, therefore, high performance rare earth intermetallic compounds reinforced Mg—Li composites are required.